The present invention relates generally to film copying systems and methods and more particularly to a system for and a method of making multiple copies of an original hologram or an original hologram itself on successive sements of a continuous length of blank film.
A system or method of the general type just recited is briefly described in APPLIED OPTICS, Vol. 5, No. 12, December 1966, p1945-1947 and in OPTICAL HOLOGRAPHY by Robert J. Collier et al, copyright 1971, p564-572, reference being made thereto. As described in the latter publication, it is important to support the hologram in a predetermined position relative to the light beam and it is important to support each successive segment of blank film (photographic emulsion) in a predetermined position relative to the hologram. In order to minimize optical distortion, the blank segment should be as close as possible to the hologram but laterally fixed relative thereto and undesirable light dispersion and reflection should be minimized as the beam passes through the two during the printing process. However, the systems which have been suggested heretofore and which applicants are familiar with, have not been completely satisfactory in this regard.
As one example, reference is made to a prior art copying system such as one disclosed in U.S. Pat. No. 3,716,268, where the hologram is supported in front of the film to be copied with its front face exposed directly to the incident beam) (or beams of light. While this exposed front face may appear perfectly smooth to the naked eye, it is more often than not quite irregular, at least relative to the wave length of the impinging light beam. As a result, the light does not pass through the hologram in an entirely predictable manner but rather is at least in part refracted in a somewhat random fashion as a result of the irregular surface thereby causing undesirable dispersion and contributing to the distortion referred to above. As will be seen hereinafter, the hologram disclosed herein is supported in a way which, from an optical standpoint, eliminates this relatively rough surface and therefore reduces distortion.
As an example of optical distortion resulting from improper support of the blank film to be copied, reference is made to a prior art copying system where the continuous length of blank film is supported in position laterally next to the hologram by mechanical means or as in the above-recited patent by means of vacuum. In those systems where the blank film is laterally supported mechanically, each segment of the film typically passes through a bath of indexing fluid and is thereafter positioned against a light transparent plate provided between the hologram and film. As the blank film segment moves up the back side of the support plate from the path, it is held in position by mechanical means such as the pressure plate. This mechanical method of supporting the blank film against the back plate has several drawbacks resulting in distortion. First, it causes distinct stress points as the film moves across the back plate which in turn produce high and low (laterally uneven) surfaces across the blank film. In most cases, the film will eventually return to its original planar configuration. However, if a copy of the hologram is made as the film returns to this stress-free configuration, which requires lateral movement of the film surface relative to the back plate and hologram, the reproduced image will most likely be distorted or, at least, its resolution will be compromised. Therefore, it is important to wait for this movement as well as all other movement adversely affecting image reproduction and/or resolution to subside. This period may be generally referred to as the "settling time" and with respect to movement caused by film strain, the settling time can take as long as 3 minutes, which of course slows down the overall process significantly.
The various disadvantages just discussed with respect to mechanical means of supporting the blank film laterally are equally applicable where the film is laterally supported by means of vacuum as described in the cited patent. This is because the same type of stress points may results. As will be seen hereinafter, in the system and method disclosed herein, the continuous length of blank film is supported to a back plate without utilizing vacuum or any mechanical means other than surface-tension and cohesive action of the index matching fluid itself. This eliminates the stress points discussed above and significantly reduces settling time as well as minimizing the possibility of abrasion.